Hydrogen that is generated entirely with power from renewable energy and the electrolysis of water; which generates no carbon pollution.

hydrogen generated from methane feedstock, typically from natural gas/petroleum gas, whose carbon residue, typically carbon dioxide, is captured, resulting in a low-carbon process.

Alternative spelling of oxyhydrogen

The solid phase of hydrogen; frozen hydrogen state / Synonym of metal hydride / A metal lattice which has absorbed hydrogen gas / Used other than figuratively or idiomatically: see solid, hydrogen.

Alternative form of gray hydrogen

hydrogen generated from hydrocarbon sources without attempting to capture and eliminate the waste carbon pollution

(physics, chemistry) An electrode with a standard electrode potential of zero; used as a standard against which other electrodes are measured.

a hydrogen electrode

(chemistry) potassium bicarbonate

(inorganic chemistry) The compound sodium hydrogen arsenate.